The proposed research will investigate early light adaptation and early dark application in the near peripheral retina of human subjects. We are particularly concerned with those stimulus conditions under which visual adaptation is determined by independent receptor mechanisms, as contrasted with those conditions in which rod and cone signals interact. We also plan to test for the role of borders versus size-tuned mechanisms in adaptation. We will analyze retinal versus cortical contributions by comparing monoptic and dichoptic measures. Our experimental approach involves an application of Stiles' two-color increment threshold technique and Crawford's early adaptation technique. We will be measuring rapid adaptation near the onset and offset of background disks, annuli, and windmills. We will also be manipulating the temporal characteristics of the adapting fields by using symmetrical or asymmetrical temporal ramps.